In recent years, semiconductor integrated circuit elements such as CPUs, and other LSIs which operate at high speeds, have been made increasingly smaller in size, and thus the number of signal terminals, power source terminals and/or ground terminals has increased, and the distance between terminals has been reduced. A popular technique involves the provision of a terminal array comprising an integrated circuit wherein a large number of terminals are connected to a mother board using so-called flip-chip connections. However, the gaps between terminals differ greatly for the terminal array of the integrated circuit as compared with the terminal array on the mother board. Because of this, an intermediate wiring board is required in eliminating this difference in the terminal spacing.
So-called organic package boards in such intermediate boards have laminated wiring portions comprising alternate dielectric layers and conductor layers made of macromolecular material, and include a terminal array for flip-chip connection arranged on a first main surface formed by the dielectric layer of the laminated wiring portion. The laminated wiring portion is formed on a board core which is principally made of macromolecular material such as an epoxy resin reinforced by glass fiber. When the terminal gap on the IC side is greatly different from the terminal gap on the side of the main board (mother board) to which the IC side is to be connected, the wiring needed for conversion, and the pattern of the connecting vias, tend to be quite small and complicated as the number of terminals involved increases. However, organic package boards have the advantage that the miniaturized and complicated wiring pattern required can be formed easily, with high definition, using a combination of photolithography and plating.
On the other hand, in such organic package boards the main board (for example, a mother board) to which connections are to be made is principally made of a macromolecular material, and, further, the organic package boards are principally made of a macromolecular material. For this reason, if the heat history, such as soldering reflow, is considered, the difference in the linear coefficient of expansion between a semiconductor integrated circuit element which is principally made of silicon (having a linear coefficient of expansion of, for example, 2 to 3 ppm/° C.) and the main board (having a linear coefficient of expansion of, for example, 17 to 18 ppm/° C.) is not sufficiently absorbed. This difference can potentially cause a defect such as peeling of the solder.
Japanese Patent Application Laid-Open No. 2001-035966 discloses a ceramic package board where a chief material used in making the board is a ceramic. When such a ceramic package board is used, the large gap in the linear coefficient of expansion between the semiconductor integrated circuit element and the main board to be flip-chip connected thereto is decreased, thereby effectively preventing the problem discussed above and, more particularly, effectively preventing a defect such as a break due to thermal stress in a soldered joint between the semiconductor integrated circuit element and the terminals.
However, with ceramic package boards, because the wiring portion is formed by using printing and calcining of a metal paste, it is more difficult to miniaturize the wiring portion, and to thus provide a highly integrated wiring board, than with organic package boards which, as noted above, can be made using lithography techniques. Thus, the amount of reduction in the terminal gaps on the side of the semiconductor integrated circuit element is limited.
A multistage board connecting structure, wherein a first intermediate board comprised of an organic package board is connected to a main board, a second “relay” board made of ceramic is connected to the first intermediate board, and a semiconductor integrated circuit element is connected to the second “relay” board, is also a potential candidate for this application. However, with this structure, it is difficult to comply with the very small size requirement because the dimension of the board connecting structure in the heightwise direction is increased by the increase in the number of the intermediate boards. Moreover, the number of connecting steps required is also increased. For this reason, the multistage board connecting structure is not an attractive candidate for this application.